U.S. patent application number 11/489359 was filed with the patent office on 2008-01-24 for substrate possessing a transparent protective layer derived from a radiation-curable acrylate composition.
Invention is credited to Jeanne E. Haubrich, Wen P. Liao, Sona Sivakova Slocum.
Application Number | 20080020170 11/489359 |
Document ID | / |
Family ID | 38692104 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080020170 |
Kind Code |
A1 |
Haubrich; Jeanne E. ; et
al. |
January 24, 2008 |
Substrate possessing a transparent protective layer derived from a
radiation-curable acrylate composition
Abstract
A substate possesses a transparent protective layer derived from
a radiation-curable acrylate composition which comprises: a) at
least one urethane polyacrylate possessing a number average
molecular weight of at least about 400 per acrylate group and
having a T.sub.g of not greater than about 40.degree. C.; b) at
least one crosslinking polyacrylate having a T.sub.g of at least
about 50.degree. C.; c) at least one hydrophobic monoacrylate; and,
d) at least one photoinitiator.
Inventors: |
Haubrich; Jeanne E.;
(Clifton Park, NY) ; Liao; Wen P.; (Clifton Park,
NY) ; Slocum; Sona Sivakova; (Malta, NY) |
Correspondence
Address: |
DILWORTH & BARRESE, LLP
333 EARLE OVINGTON BLVD., SUITE 702
UNIONDALE
NY
11553
US
|
Family ID: |
38692104 |
Appl. No.: |
11/489359 |
Filed: |
July 19, 2006 |
Current U.S.
Class: |
428/65.1 ;
428/423.1; 428/522 |
Current CPC
Class: |
Y10T 428/31935 20150401;
C08L 2312/00 20130101; C09D 133/14 20130101; Y10T 428/31551
20150401; C08L 2312/06 20130101; C08L 2666/04 20130101; C08L 33/02
20130101; C09D 133/14 20130101 |
Class at
Publication: |
428/65.1 ;
428/423.1; 428/522 |
International
Class: |
B32B 3/02 20060101
B32B003/02; B32B 27/40 20060101 B32B027/40; B32B 27/30 20060101
B32B027/30 |
Claims
1. A substrate possessing a transparent protective layer derived
from a radiation-curable acrylate composition which comprises: a)
at least one urethane polyacrylate possessing a number average
molecular weight of at least about 400 per acrylate group and
having a T.sub.g of not greater than about 40.degree. C.; b) at
least one crosslinking polyacrylate having a T.sub.g of at least
about 50.degree. C.; c) at least one hydrophobic monoacrylate; and,
d) at least one photoinitiator.
2. The substrate of claim 1 wherein urethane polyacrylate (a) is a
diacrylate or triacrylate possessing a number average molecular
weight of at least about 600 per acrylate group.
3. The substrate of claim 2 wherein the urethane diacrylate or
triacrylate is aliphatic polyester-based.
4. The substrate of claim 1 wherein the radiation-curable acrylate
composition contains from about 20 to about 70 weight percent
urethane polyacrylate (a) by weight of all the acrylate
monomers.
5. The substrate of claim 1 wherein the radiation-curable acrylate
composition comprises from about 40 to about 60 weight percent
urethane polyacrylate (a) by weight of all the acrylate
monomers.
6. The substrate of claim 1 wherein crosslinking polyacrylate (b)
is an alkoxylated bisphenol A diacrylate possessing a molecular
weight of less than about 400 per acrylate group.
7. The substrate of claim 6 wherein the bisphenol A diacrylate
contains from about 1 to about 6 ethoxylate units.
8. The substrate of claim 1 wherein the radiation-curable acrylate
composition contains from about 10 to about 50 weight percent
crosslinking polyacrylate (b) by weight of all the acrylate
monomers.
9. The substrate of claim 1 wherein the radiation-curable acrylate
conposiiton contains from about 15 to about 35 weight percent
crosslinking polyacrylate (b) by weight of all the acrylate
monomers.
10. The substrate of claim 1 wherein hydrophobic monoacrylate (c)
is at least one member selected from group consisting of
cycloaliphatic monoacrylates and long chain aliphatic
monoacrylates.
11. The substrate of claim 10 wherein the cycloaliphatic
monoacrylate is at least one member selected from the group
consisting of isobornyl acrylate, cyclohexyl acrylate,
4-t-butylcyclohexylacrylate and dihydrodicyclopentadienyl
acrylate.
12. The substrate of claim 10 wherein the long chain aliphatic
monoacrylate is at least one number selected form the group
consisting of heptylacrylate, isooctylacrylate, isodecyl acrylate,
tridecylacrylate and lauryl acrylate.
13. The substrate of claim 1 wherein the radiation-curable acrylate
composition contains form about 5 to about 30 weight percent
hydrophobic monofunctional acrylate (c) by weight of all the
acrylate monomers.
14. The substrate of claim 1 wherein the radiation-curable acrylate
composition contains form about 10 to about 20 weight percent
hydrophobic monoacrylate (c) by weight of all the acrylate
monomers.
15. The substrate claim 1 wherein photoinitiator (d) is a mixture
of alpha hydroxy ketone and arylphosphine oxide.
16. The substrate of claim 1 wherein the radiation-curable acrylate
composition contains from about 0.5 to about 5 weight percent
photoinitator(s) (d).
17. The substrate of claim 1 wherein the radiation-curable acrylate
composition contains a surfactant.
18. The substrate of claim 17 wherein the surfactant is at least
one member selected from the group consisting of silicone
surfactant and perfluoro surfactant.
19. The substrate of claim 18 wherein the silicone surfactant is a
silicone polyether.
20. The substrate of claim 18 wherein the perfluoro surfactant is a
perfluoropolyether.
21. The substrate of claim 1 wherein the radiation-curable acrylate
composition comprises: a) at least one aliphatic polyester-based
polyurethane diacrylate or triacrylate in an amount of from about
30 to about 70 by weight of all the acrylate monomers; b) at least
one alkoxylated bisphenol A diacrylate in an amount of from about
15 to about 35 by weight of all the acrylates; c) at least one
hydrophobic monoacrylate selected from the group consisting of
cycloaliphatic monoacrylate and long chain aliphatic monoacrylate
in an amount of from about 10 to about 30 percent by weight of all
the acrylate monomers; d) at least one phohotinitiator; and, e)
optionally, at least one surfactant.
22. The substrate of claim 1 wherein the transparent protective
layer possesses a modulus of not greater than about 500 MPa.
23. The substrate of claim 1 wherein the transparent protective
layer possesses a modulus of not greater than about 250 MPa.
24. The substrate of claim 1 wherein the transparent protective
layer possesses an elongation at break of at least about 8
percent.
25. The substrate of claim 1 wherein the transparent protective
layer possesses an elongated break of at least about 25
percent.
26. The substrate of claim 1 wherein the transparent protective
layer exhibits a contact angle of glycerol trioleate of at least
about 30.degree. and a finger scratch recovery time of less than
about 2 minutes.
27. The substrate of claim 1 wherein the transparent protective
layer exhibits a contact angle of glycerol trioleate of at least
about 40.degree. and a finger scratch recovery time of less than
about 1 minute.
28. The substrate of claim 21 wherein the transparent protective
layer possesses a modulus of not greater than about 500 MPa, an
elongation at break of at least about 8 percent, a contact angle of
glycerol trioleate of at least about 30.degree. and a finger
scratch recovery time of less than about 2 minutes.
29. The substrate of claim 21 wherein the transparent protective
layer possesses a modulus of not greater than about 250 MPa, an
elongation at break of at least about 25 percent, a contact angle
of glycerol trioleate of at least about 40.degree. and a finger
scratch recovery time of less than about 1 minute.
30. The substrate of claim 1 wherein the transparent protective
layer exhibits a shrinkage of less than about 8 percent.
31. The substrate of claim 21 wherein the transparent protective
layer exhibits a shrinkage of less than about 8 percent.
32. The substrate of claim 1 which is a CD, DVD, HD DVD or BD.
33. The substrate of claim 17 which is a CD, DVD, HD DVD or BD.
34. The substrate of claim 21 which is a CD, DVD, HD DVD or BD.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a substrate, and in particular, an
optical data storage medium, possessing a transparent protective
layer derived from a radiation-curable acrylate compositions.
[0002] As data storage densities are increased in optical data
storage media, e.g., compact audio discs (CD), digital versatile
discs (DVD) and the more recent high definition digital versatile
discs (HD DVD) and Blu-ray discs (BD) (so-named for the blue-violet
laser that is used to read and write to the disc), the performance
requirements for the transparent, or light-transmitting, layer of
the disc become increasingly stringent. Optical discs with
progressively shorter reading and writing wavelengths, in
particular, the aforementioned BD, have been the object of
considerable developmental effort. BD is expected to replace video
tape and the lower data storage density DVD within a few years. The
BD format is also likely to become the optical standard for
computer data storage and high-definition movies.
[0003] A typical optical disc includes a relatively thick
disc-shaped thermoplastic resin substrate, a metallic reflective
layer, a data layer and a transparent protective layer. In the case
of BD, the protective layer can be of the single layer or double
layer type, the total thickness of both types being about 100
.mu.m.
[0004] In the two layer construction, a first 97 .mu.m transparent
layer is formed on the data layer followed by formation of a second
31 .mu.m transparent hardcoat layer on the first transparent layer.
Although the first 97 .mu.m transparent layer does not provide
abrasion resistance or scratch resistance properties, the second 3
.mu.m transparent layer is intended to provide these needed
properties.
[0005] Transitioning from the aforedescribed two layer construction
to a single layer protective coating that provides abrasion
resistance and scratch resistance properties would be desirable as
it would significantly simplify the disc assembly procedure.
[0006] Abrasion resistance and scratch resistance can normally be
achieved by forming the transparent protective layer from
radiation-curable acrylate compositions which crosslink to a high
degree during the curing (i.e., polymerization) process. However,
most polymer-forming compositions will undergo shrinkage upon
polymerization. Shrinkage of the cured protective coating induces
stress between it and the substrate which in turn causes the disc
to tilt. Because of the higher data densities involved and the
necessary precision required of the laser light, particularly in
the case of BD, an excessive degree of tilt must be avoided.
[0007] It is therefore an object of the invention to provide a
substrate, e.g., an optical data storage medium radiation-curable
acrylate such as CD, DVD, HD DVD and BD possessing a transparent
protective layer obtained from s radiation-curable acrylate
composition which undergoes minimal shrinkage during curing and
remains dimensionally stable during ambient temperature
fluctuations, thus avoiding excessive tilt, while exhibiting a high
level of abrasion resistance and scratch resistance.
[0008] It is another object of the invention to provide an optical
data storage medium possessing a transparent protective layer
obtained from a radiation-curable acrylate composition which,
following its curing, will provide a transparent protective coating
of low modulus and, advantageously, high elasticity.
SUMMARY OF THE INVENTION
[0009] In accordance with the foregoing and other objects of the
invention, there is provided a substrate possessing a transparent
protective layer derived from a radiation-curable acrylate
composition which comprises:
[0010] a) at least one urethane polyacrylate possessing a number
average molecular weight of at least about 400 per acrylate
group;
[0011] b) at least one crosslinking polyacrylate;
[0012] c) at least one hydrophobic monofunctional acrylate;
and,
[0013] d) at least one photoinitiator.
[0014] When cured, e.g., by exposure to actinic radiation such as
ultraviolet (UV) light, the foregoing acrylate composition provides
a coating of low modulus and high elasticity that experiences
relatively little shrinkage during polymerization, undergoes
expansion and contraction during daily and seasonal changes in
temperature and humidity that remain within fairly tight limits and
resists abrasion and scratches by hard objects such as those of
metal. When pressure is applied, the coating tends to deform and
when pressure is released, the coating reforms thereby avoiding a
scratch.
[0015] As used herein, the term "acrylate" is inclusive of
"acrylate" and "methacrylate" functionalities.
[0016] The term "polyacrylate" refers to an acrylate possessing at
least two acrylate functionalities, e.g., diacrylate, triacrylate,
dimethacrylate, trimethacrylate, etc.
[0017] The term "Tg" refers to the glass transition temperature of
the resin derived from the acrylate(s) to which the term is
applied. Thus, e.g., the description of urethane polyacrylate (a)
in the aforedescribed radiation-curable acrylate composition as
having a Tg of not greater than about 40.degree. C. shall be
understood to mean that the glass transition temperature of the
resin derived from the polymerization of at least one urethane
polyacrylate (a) is not greater than about 40.degree. C. Similarly,
the description of crosslinking polyacrylate (b) in the
radiation-curable acrylate composition as having a Tg of at least
about 50.degree. C. shall be understood to mean that the glass
transition temperature of the resin derived from the polymerization
of at least one crosslinking polyacrylate (b) is at least about
50.degree. C.
[0018] The term "curable" shall be understood herein to mean the
full or partial curing of a composition comprising one or more
curable monomers, e.g., to at least the "green" strength of the
composition, the curing being achieved by any suitable means, e.g.,
thermal curing, curing with UV, E-beam, etc., in accordance with
known and conventional procedures.
BRIEF DESCRIPTION OF THE DRAWING
[0019] FIG. 1 is a cross sectional view of one embodiment of an
optical data storage medium possessing a transparent protective
coating layer formed from a radiation-curable acrylate composition
in accordance with the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] As shown in FIG. 1, optical data storage medium 10 is made
up of several layers including at least one substrate layer 20, at
least one data layer 30, at least one reflecting layer 40 and at
least one transparent, i.e., light-transmitting, protective layer
50.
[0021] In the context of the present disclosure, a typical optical
data storage medium possesses a number of polymeric components
which are generally combined in superimposed horizontal layers of
predetermined thicknesses whose particular values depend on the
specific properties and requirements of the data storage medium. A
major component of an optical data storage medium is a substrate
layer (part 20 in FIG. 1). The substrate layer is typically made of
a polymeric material which comprises at least one member selected
from the group consisting of thermoplastic resin, thermoset resin
and any combination thereof. Both addition and condensation
polymers are suitable for the substrate layer.
[0022] As used herein, the term "thermoplastic polymer", also
referred to in the art as a thermoplastic resin, is defined as a
material with a macromolecular structure that will repeatedly
soften when heated and harden when cooled. Illustrative classes of
useful thermoplastic polymers include styrene, acrylics,
polyethylenes, vinyls, nylons and fluorocarbons.
[0023] As used herein, the term "thermoset polymer", also referred
to in the art as a thermoset resin, is defined as a material which
solidifies when first heated under pressure and which cannot be
remelted or remolded without destroying its original
characteristics. Illustrative classes of useful thermoset polymers
include epoxides, melamines, phenolics and ureas.
[0024] Examples of useful thermoplastic polymers include
olefin-derived polymers (e.g., polyethylene, polypropylene, and
their copolymers), polymethylpentane; diene-derived polymers (e.g.,
polybutadiene, polyisoprene, and their copolymers), polymers of
unsaturated carboxylic acids and their functional derivatives
(e.g., acrylic polymers such as poly(alkyl acrylates), poly(alkyl
methacrylates), polyacrylamides, polyacrylonitrile and polyacrylic
acid), alkenylaromatic polymers (e.g., polystyrene,
poly-alpha-methylstyrene, polyvinyltoluene, and rubber-modified
polystyrenes), polyamides (e.g., nylon-6, nylon-6,6, nylon-1,1, and
nylon-1,2), polyesters; polyketones; polycarbonates; polyester
carbonates; polyethers such as aromatic polyethers, polyarylene
ethers, polyethersulfones, polyetherketones, polyetheretherketones,
polyetherimides; polyarylene sulfides, polysulfones,
polysulfidesulfones; and liquid crystalline polymers. In one
embodiment, the substrate layer comprises a thermoplastic
polyester. Suitable examples of thermoplastic polyesters include,
but are not limited to, poly (ethylene terephthalate),
poly(1,4-butylene terephthalate), poly(1,3-propylene
terephthalate), poly(cyclohexanedimethanol terephthalate),
poly(cyclohexanedimethanol-co-ethylene terephthalate),
poly(ethylene naphthalate), poly(butylene naphthalate), and
polyarylates. For example, the substrate layer can comprise a
polyester, a polycarbonate, a polystyrene, a
polymethylmethacrylate, a polyketone, a polyamide, an aromatic
polyether, a polyether-sulfone, a polyether-imide, a polyether
ketone, a polyphenylene ether, a polyphenylene sulfide, and any
combinations thereof.
[0025] In another embodiment, the substrate layer comprises a
thermoplastic elastomeric polyester (TPE). As defined herein, a
thermoplastic elastomer is a material that can be processed as a
thermoplastic material but which also possesses some of the
properties of a conventional thermoset resin. Suitable examples of
thermoplastic elastomeric polyesters include polyetheresters,
poly(alkylene terephthalate), poly(ethylene terephthalate), poly
(butylene terephthalate), polyetheresters containing soft-block
segments of poly (alkylene oxide) particularly segments of
poly(ethylene oxide) and poly(butylene oxide), polyesteramides such
as those synthesized by the condensation of an aromatic
diisocyanate with dicarboxylic acids and any polyester with a
carboxylic acid terminal group.
[0026] Optionally, the substrate layer can include at least one
dielectric layer, at least one insulating layer or any combination
thereof. The dielectric layer(s), which are often employed as heat
controllers, typically have a thickness between about 200 .ANG. and
about 1,000 .ANG.. Suitable dielectric layers include a nitride
layer (e.g., silicone nitride, aluminum nitride), an oxide layer
(e.g. aluminum oxide), a carbide layer (e.g., silicon carbide) and
any combinations comprising at least one of the foregoing and any
compatible material that is not reactive with the surrounding
layers.
[0027] A typical optical disc includes at least one data layer
(part 30 in FIG. 1). The data layer can be made of any material
that is capable of storing optically retrievable data such as an
optical layer or a magneto-optic layer. The thickness of a typical
data layer can be up to about 600 .ANG.. In one embodiment, the
thickness of the data layer is up to about 300 .ANG.. The
information which is to be stored on the data storage medium can be
imprinted directly onto the surface of the data layer or stored in
a medium which has been deposited onto the surface of the substrate
layer. Suitable data storage layers are typically composed of at
least one material selected from the group consisting of oxides
(e.g., silicone oxide), rare earth element-transition metal alloys,
nickel, cobalt, chromium, tantalum, platinum, terbium, gadolinium,
iron, boron, organic dyes (e.g., cyanine or phthalocyanine type
dyes), inorganic phase change compounds (e.g., TeSeSn or InAgSb)
and any alloys or combinations comprising at least one of the
foregoing.
[0028] The reflective metal layer(s) (part 40 in FIG. 1) should be
of a thickness that is sufficient to reflect an amount of energy
sufficient to enable data retrieval. Typically, a reflective layer
has a thickness up to about 700 .ANG.. In one embodiment, the
thickness of the reflective layer is between about 300 .ANG. and
about 600 .ANG.. Suitable reflective layers include aluminum,
silver, gold, titanium and alloys and mixtures comprising at least
one of the foregoing.
[0029] The transparent protective layer (part 50 in FIG. 1) is
obtained by the radiation curing of a radiation-curable acrylate
composition in accordance with the invention. The radiation-curable
acrylate composition comprises:
[0030] a) at least one urethane polyacrylate possessing a number
average molecular weight of at least about 400 per acrylate group
and having a Tg of not greater than about 40.degree. C.;
[0031] b) at least one crosslinking polyacrylate having a Tg of at
least about 50.degree. C.;
[0032] c) at least one hydrophobic monoacrylate; and,
[0033] d) at least one phohoinitiator.
[0034] When, following curing of the radiation-curable acrylate
composition herein, urethane polyacrylate (a) become chemically
integrated with the other acrylate monomers in the structure of the
resulting resin, it contributes several properties thereto which
are particularly desirable for its use as the protective coating of
an optical data storage medium. Among these properties are good
abrasion resistance and scratch resistance, reduced shrinkage and
enhanced flexibility.
[0035] Urethane polyacrylate (a) is advantageously a diacrylate or
triacrylate possessing a number average molecular weight in one
embodiment of at least about 600 per acrylate group, in another
embodiment of at least about 800 per acrylate group and still in
another embodiment, a Tg of not greater than about 30.degree. C.
These and other useful urethane polyacrylates are known and in
general are obtained by reaction of an isocyanate-terminated
polyurethane (itself obtained from the reaction of a polyol such as
a polyether polyol or a polyester polyol with a slight molar excess
of organic polyisocyanate) with a hydroxyl-terminated acrylate such
as hydroxyethyl acrylate, hydroxyethyl methacrylate, and the like.
Assuming an equimolar reaction of isocyanate-terminated
polyurethane and hydroxyl-terminated acrylate, the average number
of acrylate groups in the urethane polyacrylate will correspond to
the average number of isocyanate groups in the
isocyanate-terminated polyurethane.
[0036] Particularly suitable for use herein are the aliphatic
polyester-based urethane diacrylates and triacrylates, a number as
which are commercially available from such companies as Rahn US
Corp., Sartomer Company, Inc., Cytec Industries, Inc. and Bomar
Specialties Co. among others. Also useful are urethane
polyacrylates which have been diluted with low viscosity acrylates
to reduce their viscosities such as Ebecryl 230 (aliphatic urethane
diacrylate having a viscosity of about 40,000 cps), Ebecryl 244
(aliphatic urethane diacrylate diluted with 10 weight percent
1,6-hexanediol diacrylate), Ebecryl 284 (aliphatic urethane
diacrylate diluted with 10 weight percent 1,6-hexanediol
diacrylate), all available from UCB Chemicals, CN-963A80 (aliphatic
urethane diacrylate blended with 20 weight percent tripropylene
glycol diacrylate), CN-966A80 (aliphatic urethane diacrylate
blended with 20 weight percent tripropylene glycol diacrylate),
CN-982A75 (aliphatic urethane diacrylate blended with 25 weight
percent tripropylene glycol diacrylate) and CN-983 (aliphatic
urethane diacrylate), all available from Sartomer Corp.
[0037] In general, the amount of urethane acrylate (a) in the
radiation-curable acrylate composition will be sufficient to impart
the desirable properties to the cured resin that are mentioned
above, in particular, good abrasion resistance and scratch
resistance, reduced shrinkage and enhanced flexibility.
[0038] Crosslinking polyacrylate (b) imparts or contributes to
several useful properties of the cured resin including reduced
tack, increased glass transition temperature (Tg) and decreased
gas, in particular, water vapor, permeability. One class of
crosslinking polyacrylate (b) that has been found to provide
particularly good results are the alkoxylated phenolic diacrylates,
in one embodiment, those possessing an average molecular weight of
less than about 400 per acrylate group, in another embodiment, less
than 350 per acrylate group, and still in another embodiment, a Tg
of at least about 60.degree. C. Specific diacrylates of this type
include ethoxylated (1) bisphenol A diacrylate, ethoxylated (1)
bisphenol A dimethacrylate, ethoxylated (2) bisphenol A diacrylate,
ethoxylated (2) bisphenol A dimethacrylate, ethoxylated (3)
bisphenol A diacrylate, ethoxylated (3) bisphenol A dimethacrylate,
ethoxylated (4) bisphenol A diacrylate, ethoxylated (4) bisphenol A
dimethacrylate, and the like, as well as their mixtures.
[0039] In general, crosslinking polyacrylate(s) (b) can be present,
in a first embodiment, at a level of from about 10 to about 50
weight percent, and in a second embodiment, at a level of from
about 15 to about 35 weight percent, by weight of the entire
monomer mixture.
[0040] Hydrophobic monoacrylate(s) (c) in the radiation-curable
acrylate composition also contribute to the low water vapor and
moisture absorption properties of the cured resin. In an optical
disc, it is of particular importance to minimize permeation of
water vapor and moisture as they may degrade the integrity of the
reflecting layer and consequently the readability of the recorded
data. The useful hydrophobic monoacrylates include those derived
from aliphatic alcohols, e.g., of the cycloaliphatic (monocyclic,
bicylic, etc.) and long chain aliphatic (e.g., chain length of from
about 8 to about 22 carbon atoms) varieties. Useful hydrophobic
cycloaliphatic monoacrylates (c) include isobornyl acrylate,
cyclohexyl acrylate, 4-t-butylcyclohexylacrylate,
dihydrodicyclopentadienyl acrylate, and the like, and their
mixtures. Useful hydrophobic long chain aliphatic monoacrylates (c)
include heptyl acrylate, isooctyl acrylate, isodecyl acrylate,
tridecyl acrylate, lauryl acrylate, and the like, and their
mixtures.
[0041] Any of the photoinitiators heretofore employed in the curing
of acrylate-containing compositions can be used as
photoinitiator(s) (d) herein. Examples of useful photoinitiators
that can be used include 2-hydroxy-2-methyl-1-phenyl-propan-1-one,
2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one and
blends of 1-hydroxycyclohexylphenyl acetone and diphenyl
(2,4,6-trimethylbenzoyl) phosphine oxides. The photoinitiator(s)
can be present in amounts of from about 0.25 to about 10 weight
percent of the radiation-curable acrylate composition and are
advantageously present therein at from about 2 to about 5 weight
percent.
[0042] The viscosity of the totally formulated radiation-curable
acrylate composition should be such as to facilitate its
application without the need to add solvent or other non-reactive
viscosity reducing component. In general, the radiation-curable
acrylate composition herein can possess a viscosity of from about
500 to about 5000 cps at 25.degree. C. and, advantageously, of from
about 1000 to about 3000 cps at 25.degree. C.
[0043] The radiation-curable acrylate composition can contain one
or more optional components to impart yet additional desirable
properties to the cured resin obtained therefrom. One especially
useful class of additives is surfactants, in particular, silicone
surfactants and perfluoro surfactants which, when added to the
radiation-curable acrylate compositon, impart one or more
additionally desirable properties to the cured resin such as
resistance to fingerprints (i.e., antifingerprint capability) and
other kinds of smudging, increased surface slip for improved
abrasion resistance and improved coating uniformity, or leveling.
In general, a surfactant can be present in the radiation-curable
acrylate composition at a level of from about 0.05 to about 10
weight percent and, advantageously, at a level of from about 0.1 to
about 2 weight percent. In one embodiment, a silicone surfactant
such as a silicone polyether surfactant, and in another embodiment,
a perfluoropolyether surfactant, can be utilized to impart an
antifingerprint property to the cured resin. For example, Silwet
L7657 (General Electric), a silicone polyether surfactant in which
the polyether moiety is a poly(ethyleneoxide) chain, and Zonyl FSN
(DuPont), a perfluoropolyether disclosed in U.S. Pat. No.
5,609,990, the contents of which are incorporated by reference
herein, can be utilized within the aforestated amounts to confer
antifingerprint capability upon the cured resin, an especially
desirable property when the resin functions as the transparent
protective layer of an optical data storage medium.
[0044] The cured resin obtained from the foregoing
radiation-curable acrylate composition will possess a level of
transparency enabling it to function as the protective coating of
an optical data storage medium in accordance with the invention.
Thus, for example, the cured acrylate coating will exhibit a
transparency as measured by UV-Vis spectrameter in a first
embodiment of at least about 90 percent and in a second embodiment
of at least about 95 percent.
[0045] The cured resin constituting the transparent protective
layer of the substrate herein exhibits a characteristically low
modulus, understood as a tensile modulus of not greater than about
500 Mpa and, advantageously, of not greater than about 250 Mpa. In
other embodiments, the cured resin will also exhibit a high
elasticity, understood as an elongation at break of at least about
10 percent and, advantageously, of at least about 25 percent.
[0046] Other useful properties of the cured resin include a
shrinkage of less than about 8 percent and, advantageously, of less
than about 5 percent, a scratch resisitance are measured by the
change in haze following Taber abrasion testing of less than about
5 percent and, advantageously, of less than about 2 percent, and a
Tg of from about 20.degree. to about 60.degree. C. and,
advantageously, from about 35 to about 50.degree. C.
[0047] Still other desirable properties of the cured resin include
a moisture absorbance (water pick-up) of not greater than about 1.5
weight percent, a contact angle with glycerol trioleate of at least
about 30.degree. and, advantageously, of at least about 45.degree.,
a surface resistivity of not greater than about 1.times.10.sup.-14
Ohms, a change in reflectivity following accelerated aging testing
of less than about 20 percent and, advantageously, of less than
about 10 percent, a relative birefringence, initially and following
accelerated aging testing, of less than about 20 and,
advantageously, of less than about 15.
[0048] The cured resin layer can be formed on the optical disc
herein employing any of the known and conventional procedures. In
one embodiment, the cured resin layer is obtained by applying a
coating of radiation-curable coating composition to a disc to a
predetermined thickness employing the known procedure of
spincoating and at some time during or following the spincoating
operation, exposing the composition to radiation, e.g., UV-light,
under conditions that will achieve its cure. In one embodiment, the
radiation-curable composition is applied to the disc surface
employing a spin rate of from about 500 to about 3000 rpm for from
about 1 to about 30 seconds and thereafter cured. A typical curing
operation involves the use of a Fusion D or H bulb with a set
intensity ranging between 1.384-2.8 W/cm.sup.2 and a dosage of
0.304-2 J/cm.sup.2 or Xenon Flash Bulb.
[0049] The thickness of the transparent protective layer can vary
over fairly wide limits depending on the nature of the substrate to
which it is applied and the functional requirements of the layer.
In the case of optical data storage media, the thickness of this
layer can, depending on the specific type of data storage medium,
vary from about 50 to about 200 m and commonly from about 70 to
about 120 m. In the particular case of BD, the thickness of the
transparent protective layer will be on the order of about 100
m.
[0050] The entire desired thickness of curable resin can be
provided in a single operation or in a series of spincoating/curing
cycles wherein the desired thickness is built up in two or more
stages. In the latter case, it may be advantageous to only
partially cure a layer before applying the next layer and only
completing the cure following the deposition of the last layer. The
invention also contemplates the use of the radiation-curable
acrylate composition to provide only the uppermost portion of the
protective layer, e.g., the uppermost 2-10 m of the protective
layer, the greater part of the protective layer being provided by
any of the radiation-curable compositions heretofore known to
provide the transparent protective coating of an optical disc.
[0051] Regardless of the technique employed for laying the
acrylate-curable coating composition on the surface of the optical
data storage medium, and particularly in the case of a high
definition optical disc such as BD, it is desirable to maintain a
highly uniform thickness of the coated composition, and hence the
thickness of the resulting cured resin. In one embodiment, coating
uniformity should be within about 5 percent and, advantageously,
within about 3 percent, of the total average coating thickness.
[0052] An optical data storage disc possessing a transparent
protective layer in accordance with the invention will
advantageously further exhibit (1) an absolute value of the change
in tilt following accelerated aging testing of not more than about
0.8.degree. and, advantageously, of not more than about
0.5.degree., as measured at 55 mm radius, (2) an absolute value of
change in tilt following humidity shock testing of not more than
about 0.8.degree. and, advantageously, of not more than about
0.5.degree., as measured at 55 mm radius, and (3) an absolute value
of the change in tilt following heat shock testing of not more than
about 0.8.degree. and, advantageously, of not more than about
0.5.degree., as measured at 55 mm radius.
[0053] In the examples below, Examples 1-9 are illustrative of the
invention while Comparative Examples 1 and 2 (illustrating the use
of a hydrophilic monoacrylate monomer) are outside the scope of the
inveniton. In all of the examples, a series of UV-curable acrylate
compositions were prepared and spin coated on 60 mm radius disc
substrates molded from polycarbonate OQ1030 (GE Plastics) or Noryl
EXNL0090 (GE Plastics). Both of these substrates and substrates
sputtered with silver alloy were used for coating. Coating
thickness was adjusted to be about 100 m. Spincoating conditions
varied based on the viscosity of the curable composition. Typical
spincoat conditions were dispensing curable composition at the
inner diameter (ID) of the disc, ramping to about 2000 rpm in 1
second and dwelling at this speed for 3 seconds. The curable
compositions were typically cured for 2 sec using a Xenon RC-747
pulsed UV system equipped with a type D lamp.
[0054] Radial deviation and reflectivity of a cured resin coating
were measured using a Dr. Schenk PROmeteus MT-200/Blu-ray
instrument. Negative radial deviation occurs when the disc is
concave on the coating side and positive deviation occurs when the
disc is concave on the non-coated side of the disc.
[0055] For accelerated aging testing, discs were stacked on a
spindle, coated side down, with a 1.7 mm ID, 3.0 mm OD and a Teflon
washer was placed between each disc. The discs were placed in a
humidity chamber employing the following temperature and humidity
program: (1) ramp two hours from 25.degree. C. to 80.degree. C. and
from 50% relative humidity (RH) to 8% RH; (2) 80.degree. C., Ramp 2
hours to 85% RH, 3) 96 hours at 80.degree. C., 85% RH; (4)
80.degree. C., ramp 2 hours to 50% RH; (5) 6 hours at 80.degree.
C., 50% RH 6) ramp 2 hours to 25.degree. C., 50% RH; (7) 36 hours
at 25.degree. C., 50% RH. Changes in tilt and reflectivity were
recorded employing the Dr. Schenk instrument.
[0056] To test if discs would undergo corrosion of their metal
layer due to the presence of fingerprints on the protective layer,
five fingerprints were made on a disc by firmly pressing with a
thumb on the protective layer for about a second such that a
clearly discernable print was left on the disc surface. The discs
were then subjected to the aging test at 80.degree. C., 85% RH
described above. After removal from the humidity chamber, discs
were analyzed to determine whether corrosion could be observed on
the metal layer beneath the areas with the fingerprints. The number
of fingerprints that exhibited observable corrosion of the
underlying metal layer was recorded.
[0057] A fingernail scratch recovery test was carried out as
follows. A thumbnail was used to make a deep impression in the
protective coating. The area was then wiped clean and the
impression observed to determine the number of minutes required for
the scratch to no longer be visible. An acceptable scratch recovery
time is less than 2 minutes and a preferred recovery time is less
than 1 minute.
EXAMPLE 1
[0058] A UV-curable acrylate composition was prepared by combining
and uniformly mixing Genomer 4316 (52.0 parts, available from Rahn
USA), ethoxylated (4) bisphenol A diacrylate (30.0 parts), Irgacure
184 (2.0 parts, available from Ciba), Genocure TPO (0.2 parts,
available from Rahn USA), Silwet L7657 (0.25 parts, available from
GE) and isodecyl acrylate (15.5 parts). The composition was coated
on a silver-coated Noryl disc and aged at 80.degree. C. at 85% RH
as described above.
EXAMPLE 2
[0059] A UV-curable acrylate composition was prepared and coated as
in Example 1 except that isobornyl acrylate was used in place of
isodecyl acrylate.
EXAMPLE 3
[0060] A UV-curable acrylate composition was prepared and coated as
in Example 1 except that 1.5 weight % Irgacure 184 was used instead
of 2 weight % Irgacure 184, and a predominantly hydrophobic blend
of 50 weight % isodecyl acrylate and 50 weight % phenoxyethyl
acrylate, a hydrophobic monoacrylate, was used in place of isodecyl
acrylate.
EXAMPLE 4
[0061] A UV-curable acrylate composition was prepared and coated as
in Example 1 except that 1.5 weight % Irgacure 184 was used instead
of 2 weight % Irgacure 184 and a predominantly hydrophobic blend of
75 weight % isodecyl acrylate and 25 weight % 2-phenoxyethyl
acrylate was used in place of isodecyl acrylate.
EXAMPLE 5
[0062] A UV-curable acrylate composition was prepared and coated as
in Example 1 except that a blend of 50 weight % isobornyl acrylate
and 50 weight % isodecyl acrylate was used in place of isodecyl
acrylate.
EXAMPLE 6
[0063] A UV-curable acrylate composition was prepared and coated as
in Example 1 except that a blend of 25 weight % isobornyl acrylate
and 75 weight % isodecyl acrylate was used in place of isodecyl
acrylate.
COMPARATIVE EXAMPLE 1
[0064] A UV-curable acrylate composition was prepared and coated as
in Example 1 except that an equal weight amount of
tetrahydrofurfuryl acrylate, a hydrophobic monoacrylate, was used
in place of isodecyl acrylate.
COMPARATIVE EXAMPLE 2
[0065] A UV-curable acrylate composition was prepared and coated as
in Example 3 except that 100 weight % 2-phenoxyethyl acrylate was
used in place of the blend of 50 weight % isodecyl acrylate and 50
weight % 2-phenoxyethyl acrylate.
[0066] The results of the aforedescribed tests carried out upon the
coated discs of Examples 1-8 are set forth below in Table 1
TABLE-US-00001 TABLE 1 Number of Fingernail Fingerprints Radial
Scratch Water Resulting in Deviation % Reflectivity Recovery
Example Monoacrylate Pick-up Corrosion Initial After aging Initial
After aging Time 1 IDA 0 0.04 -0.58 32.2 28.0 <1 min 2 IBOA 0
-0.02 -0.62 29.9 25.5 >2 min 3 50% IDA, 50% PhEA 0 0.04 -0.43
32.3 28.4 <1 min 4 75% IDA, 25% PhEA 1 0.03 -0.44 32.3 28.7
<1 min 5 50% IBOA, 50% IDA 0 -0.01 -0.58 32.0 28.1 >2 min 6
75% IDA, 25% IBOA 1.31 1 0.01 -0.61 31.8 27.9 <2 min. 7 THFA
1.68 5 -0.05 -0.77 31.2 26.4 <1 min 8 PhEA 5 0.01 -0.47 32.0
28.0 <1 min IDA: isodecyl acrylate; IBOA; isobornyl acrylate;
PHEA: 2-phenoxyethyl acrylate; THFA: tetrahydrofurfuryl
acrylate.
[0067] As the test data in Table 1 show, the cured resins of
Examples 1-6 which were prepared with individual monoacrylates or
with monoacrylate blends that were entirely or at least
predominantly hydrophobic in character passed the fingerprint
corrosion test while those that were prepared with a hydrophobic
monoacrylate failed the test.
[0068] In Examples 7-9 below, the preparation and testing of the
coated discs followed the general procedures described above except
as specifically noted.
[0069] Surface resistivity was measured on a cured composition of
about 100 m thickness on a polycarbonate disc employing
resistance/resistivity probe Model 803B and Keithley 8487
Picoammeter from Electro-tech Systems.
[0070] Elongation at break was measured on a dumbbell-shaped sample
cut from a 100 m thickness cured coating using Instron 4665. The
elongation when the sample broke was measured as the elongation at
break.
[0071] Percent light transmittance was measured on a cured
composition of about 100 m thickness coated on a clear
polycarbonate disc. An uncoated clear polycarbonate disc was used
as a reference at measurement. A Cary 500 Scan UV-VIS-NIR
spectrophotometer was used for the measurement.
[0072] Heat shock was performed by measuring the tilt change of a
coated disc at 70.degree. C. The tilt was measured as a mean radial
deviation at 55 mm radius using the Dr. Schenk MT-200 PROmeteus
instrument. After the initial tilt was measured, a coated BD was
placed in a 70.degree. C. oven sitting vertically in a metal rack.
The disc was removed from the oven to measure the tilt at ambient
conditions at a pre-determined interval of time. The disc was
quickly placed back in the oven after making the measurement in
order to minimize heat loss. A number of measurements were made to
establish tilt change as a function of time. The maximum change of
tilt from that before heating at 70.degree. C. was recorded as the
heat shock.
[0073] Humidity shock measures the tilt change of a coated disc
experiencing humidity changes. A coated BD was placed in a humidity
chamber set at 25.degree. C. and 90% RH for at least 4 days to
ensure that the disc was fully saturated with water vapor. The tilt
of the disc, measured as a mean radial deviation at 55 mm radius
with Dr. Schenk MT-200 PROmeteus, was measured immediately after
the disc was removed from the chamber. The tilt was monitored every
hour for 8 hours. The maximum change of the tilt from the initial
tilt was recorded as the humidity shock.
[0074] Taber abrasion resistance was measured according to ASTM
D1044-99. CS-10F wheel at load of 250 g running for 5 cycles was
used for this measurement.
EXAMPLE 7
[0075] A UV-curable acrylate composition prepared as in Example 6
was spin coated on a disc as described above except that instead of
curing the disc only after the spinning had stopped, the spinning
was slowed to about 400 rpm whereupon the coating was partially
cured using a 250W arc lamp while spinning continued. Spinning was
then stopped and the curing of the coating completed employing 20
pulses of light from a Xenon Model RC801 exposure unit equipped
with a D bulb.
EXAMPLE 8
[0076] A UV-curable acrylate composition was prepared containing
100 g of the formulation of Example 6 and 0.4 g of FSO100
fluorocarbon surfactant (DuPont). The composition was coated on a
disc as in Example 1 except that instead of curing for 2 sec (20
pulses) with a Xenon RC-747 pulsed UV system, the sample was cured
for 30 pulses utilizing a Xenon RC801 exposure unit equipped with a
D bulb.
EXAMPLE 9
[0077] The UV-curable coating composition of Example 7 was coated
on a disc as described therein except that the coating was partly
cured while spinning at about 400 rpm using a 250W arc lamp with
curing completed with 30 pulses employing a Xenon RC801 exposure
unit equipped with a D bulb.
[0078] The results of testing the coated discs of Examples 7-9 are
set forth below in Table 2.
TABLE-US-00002 TABLE 2 Property Example 7 Example 8 Example 9
Coating Tg 37.degree. C. Coating Modulus 169 Mpa Coating Elongation
at Break 40% Coating Shrinkage after Cure 4.1% Coating Taber
Abrasion Delta Haze 2.7% 1.7% Coating Contact Angle, glycerol
trioleate 51.5.degree. Coating Transmission at 405 nm 95% Coating
Moisture Pick-up 1.3% Disc Surface Resistivity 2.9 .times.
10.sup.12 Ohm/square Disc Delta Radial Deviation after curing 0.01
0.06 0.15 Disc Delta Radial Deviation after aging for 4 days, -0.29
-0.76 -0.40 80.degree. C. at 85% RH Disc Delta Radial Deviation
after aging for 5 days at 0.18 0.37 -0.45 25.degree. C., 90% RH
Disc Delta Radial Deviation after heat shock 0.27 0.05 0.04 Coating
Fingernail Scratch Recovery Time <1 min Number of Fingerprints
Resulting in Corrosion 0 Disc Coating Thickness Range 97 103
microns 97 103
[0079] While the invention has been described with reference to
certain embodiments, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out the process of the invention, but that the invention
will include all embodiments falling within the scope of the
appended claims.
* * * * *